1. Field of the Invention
The present invention belongs to a field of electric contacts and electric connectors, and relates to an electric contact and an electric connector, which are mounted on a printed circuit board by inserting into a through hole or a concaved part of the printed circuit board.
2. Related Art
The so-called dip type electric contact is known. It is made of metal sheet and comprises a protruding part, which is inserted into a through hole in a printed circuit board, and a barrel, to which an electric wire is connected. This electric contact is mounted on a printed circuit board by inserting its protruding part into a through hole in the printed circuit board and soldering the protruding part to the conductor which is penetrated by the through hole.
When the above-mentioned conventional electric contact is to be mounted on a printed circuit board by soldering, molten solder will be applied to the protruding part. However, if another part is mounted close to the electric contact on the printed circuit board, it may be difficult or impossible to solder the electric contact. Further, if some electric contacts are held in a housing to make an electric connector, the housing may interfere and make it difficult to solder the electric contacts onto a printed circuit board. Moreover, this work of applying solder requires careful solder quality control, temperature control and the like, and the man-hours required for control are increased correspondingly. If the electric contact is microminiaturized to connect with, for example, a very fine wire (for example, American Wire Gauge size 36 falls in the category of very fine wire, and the diameter of this electric wire is approximately 0.12 mm), the work of applying molten solder to the protruding part cannot be done by an automatic machine, and it is necessary to do the work manually by a skilled worker. Hence the productivity is low, and this results in an increase in cost.
In that case, these problems may be solved by forming the protruding part so that it can be pressed into the through hole, and in turn, eliminating the need of soldering. Measures to secure a force for pressing the protruding part into the through hole include, for example, making the protruding part into a cylinder and making longitudinal slits in the cylinder to induce easier deformation of the cylinder, and providing the cylinder with ribs. However, such protruding parts may be difficult to work on and produce, and even if they can be produced, they pose a problem of high cost because complicated working processes are required.
Now, Japanese Patent unexamined publication gazette Heisei 10-237331 discloses a lead-free ultrahigh-conductive plastic being a conductive resin composite, comprising a thermoplastic resin, a lead-free solder that can be melted in the plasticated thermoplastic resin, and powder of a metal that assists fine dispersion of the lead-free solder in the thermoplastic resin or a mixture of the powder of the metal and short fibers of a metal.
This lead-free ultrahigh-conductive plastic exhibits high conductivity, for example, 10xe2x88x923xcexa9xc2x7cm or under in volume resistivity. Moreover, this material can be molded by injection molding and has a high degree of freedom in molding. Furthermore, as this material contains solder, there is no need of separately applying solder. One objective of the present invention is to provide an electric contact and an electric connector, which can solve the above-mentioned problems, and a method of connecting these electric contact and electric connector to a printed circuit board by utilizing the lead-free ultrahigh-conductive plastic, which has such excellent conductivity and moldability and contains solder.
To accomplish the above-mentioned objective, an electric contact using resin solder according to the present invention is the electric contact, which is connected to a printed circuit board, which has a conductor being provided on a surface or in an intermediate layer and a through hole or a concaved part, which penetrates the conductor, the electric contact comprises a protruding part, which is inserted into the through hole or the concaved part, and a connecting part, which is connected to a conductor of a counterpart member, and at least a part of the protruding part, which connects to the conductor of the printed circuit board, is made of a lead-free ultrahigh-conductive plastic being a conductive resin composite, comprising a thermoplastic resin, a lead-free solder that can be melted in the plasticated thermoplastic resin, and powder of a metal that assists fine dispersion of the lead-free solder in the thermoplastic resin or a mixture of the powder of the metal and short fibers of a metal.
When the protruding part of this electric contact is inserted into a through hole or a concaved part of the printed circuit board and the protruding part is heated, the lead-free solder being contained in the lead-free ultrahigh-conductive plastic of the protruding part will melt out and stick to the conductor of the printed circuit board. When the solder cools and solidifies, the electric contact will be mounted on the printed circuit board. Hence the work of separately applying solder is not required. Accordingly, even when it is difficult or impossible to solder the electric contact, for example, when another part is mounted too close to the electric contact, the electric contact can be mounted on the printed circuit board. Moreover, as solder quality control, temperature control and the like are not required, the control man-hour is reduced correspondingly. Further, even if the electric contact is microminiaturized, the mounting of the electric contact can be executed by an automatic machine. Hence the productivity is increased and the cost is reduced. The lead-free ultrahigh-conductive plastic exhibits high conductivity, as high as 10xe2x88x923xcexa9xc2x7cm or under in volume resistivity. Hence the electric resistance of the electric contact can be lowered. Moreover, after the connection of the electric wire, when electricity is passed at a normal level, the lead-free ultrahigh-conductive plastic will not melt out due to heat generation. Further, in comparison with the technology of MID (Molded Interconnection Devices, for example, refer to Registered Utility Model gazette no. 2597015), wherein a conductive plated layer is formed on the surface of an insulator, the lead-free ultrahigh-conductive plastic provides the conductor with a larger cross-sectional area and a larger volume. Hence the resistance of the conductor can be reduced and the heat dissipation is better. This, in turn, allows passage of a larger current. Moreover, as the lead-free ultrahigh-conductive plastic can be molded by injection molding, it gives a greater freedom in molding. Hence it is easy to form a part or the entirety of the protruding part into a configuration which is suited to being pressed into a through hole, and this does not cause an increase in cost due to complication of the production processes. In such a case, the electric contact can be mounted on a printed circuit board by simply pressing the protruding part into the through hole. In that case, when the protruding part is heated, the strength of connection between the protruding part and the conductor of the printed circuit board will be enhanced by the above-mentioned connecting function of the lead-free solder. Moreover, as the degree of freedom in molding is high, it is easy to obtain impedance matching. When only a part of the electric contact is made of the lead-free ultrahigh-conductive plastic, if other parts are made of a conductive material of which strength and elasticity are higher than those of the lead-free ultrahigh-conductive plastic, such as a metal, the strength and elasticity of the electric contact will be increased.